As the efficacy (measured in lumen per Watt) and the luminous flux (measured in lumen) of light emitting diodes (LEDs) continues to increase and prices continue to go down, LED illumination and LED-based luminaires are becoming viable alternatives to and at a competitive level with until now predominant common light bulbs or tube luminescent based lamps for providing large-area illumination.
By using LEDs it is possible to decrease the energy consumption, a requirement which is well in line with the current environmental trend. As a further consequence of having the possibilities to provide bright light even when using compact LEDs, a number of different lighting system have been proposed greatly differing from the standard lighting system comprising a common light bulb. In line with this and by means of using LEDs instead of light bulbs, a user is also given a more flexible control of the lighting system illumination functionalities, for example in relation to intensity dimming control of beam direction.
An example of such a lighting system is disclosed in WO 2011039690, describing a modular luminaire 100 comprising two light-emitting portions 102 and 104, as shown in FIG. 1. The two portions are individually controllable and are configured to provide complementary beam patterns. The portion 102 is configured to emit a relatively narrow beam of light illuminating a narrow, task, area. The portion 104 is configured to emit a relatively wide, batwing-type beam of light providing ambient illumination of a background area surrounding the task area. Such a split beam luminaire enables a local dimming lighting solution with higher energy savings, lower cost, and a higher comfort level than conventional office luminaires.
With a split beam luminaire, preserving the beam patterns is important. The luminaire 100 achieves preservation of the beam patterns by having the multiple light sources and their corresponding optics 106 configured to allow generation of the narrow beam pattern arranged in a separate lighting chamber, apart from the multiple light sources and their corresponding optics 108 configure to allow generation of the batwing-type pattern. This, however, provides limitations with regard to the appearance of the luminaire as such a separation of the narrow-beam and the wide-beam sources results in different appearance of the luminaire if viewed from different angles.
What is needed in the art is a split beam luminaire capable of providing more uniform luminance of the luminaire's light-emitting surface while preserving the beam patterns of the narrow and wide beams.